A chuck is normally used to hold a rotary tool and can also be used to hold a workpiece in some situations. A standard drill chuck has a chuck body on which a plurality, normally three, of angularly equispaced jaws are displaceable for clamping the tool or workpiece. It is standard practice to provide a tightening sleeve on the chuck body which when rotated in one rotational sense moves the jaws radially toward each other and when rotated in the opposite sense allows them to move radially apart.
It is possible to mount the jaws on the tightening sleeve and to set the tightening rotation direction of the sleeve opposite the rotation direction of the chuck, so that when the rotation of the tool held by the chuck is resisted this force is transformed into a force tending to tighten the jaws on the tool. Such an arrangement can be seen in German Utility Models 7,222,008 and 7,524,037 as well as in German Patent Publications 2,133,142 and 2,639,214. These self-tightening chucks are extremely advantageous in that they do not require a separate tightening key to ensure that the workpiece will be firmly held, but can easily be tightened on and loosened from a tool by hand.
A considerable disadvantage of such a chuck is that when used in a hammer drill, where is it axially reciprocated as well as rotated, and wherein in some situations it is not rotated at all but is only reciprocated, the chuck loosens. It is therefore necessary in this application to retighten the chuck frequently.